Development of a comprehensive system for the treatment of benign and malignant extracranial tumors with stereotactically directed radiation beams is proposed. Phase one research includes the design, construction and testing of a patient localization and immobilization device with associated hardware and software necessary to introduce a spinal radiosurgery system into the clinical environment. This device will allow extremely accurate radiation targeting with random geometric uncertainty less than 1.75 millimeters in the worst scenario. High targeting accuracy spares healthy tissue by decreasing the required radiation field size and increases the dose that can be safely delivered to a tumor. Initial emphasis is on treating cancers of the spine where targeting accuracy is of highest importance but there is great innovative potential to treat tumors throughout the chest and abdomen. In a percutaneous procedure, at least three radio-opaque markers are permanently affixed to the bone of the vertebral column. Markers provide a rigid reference frame from which tumor coordinates are defined. Marker locations are determined from daily biplanar radiographs and tumor coordinates are adjusted using rigid body rotation principles. Alignment lasers are used to bring the tumor to the radiation isocenter of a medical linear accelerator for treatment. PROPOSED COMMERCIAL APPLICATIONS: Research will lead to a clinic-ready localization and immobilization device to perform extracranial stereotactic radiosurgery and radiotherapy primarily in the region of the spinal column. Neurosurgeons and radiation oncologists alike would have strong interest in such a system. Everyone who is presently doing cranial based stereotactic radiosurgery would be an immediate candidate for this system including 250 Radionics XKnife sites which already exist. Sites are continually being added as domestic and international markets expand.